The present invention relates to alignment of antenna polarization axes and, in particular, it concerns alignment of antenna polarization axes of a dual polarized end-user terminal.
Geostationary satellite transponders are in common orbit 23,000 miles above the earth. The satellites share common latitude on the equator and are spaced apart longitudinally in an orbital arc, called the Clark belt, sometimes by less than one degree. When communicating with these satellites care must be taken not to illuminate more than one satellite with up-link radio frequency energy and, conversely, not to receive interfering signals from adjacent satellites located along the Clark belt. A satellite communicates using various frequencies to maximize the communication capacity of the satellite. Moreover, a satellite also typically communicates in two polarization axes, being orthogonal to each other, to maximize the capacity of each available frequency. Regulatory authorities, such as the FCC and ETSI require that the end-user terminal be aligned very accurately with the satellite. The regulations require that other satellites and also a non-designated polarization axis of the designated satellite will not receive even a component of the transmitted signal from the end-user terminal that exceeds a very low threshold. Therefore it is essential for the azimuth, elevation and polarization alignment of the end-user terminal to be aligned accurately. As is known in the art, azimuth and elevation alignment can be performed by adjusting the antenna direction of the end-user terminal to maximize the received signal from the designated satellite. This is known as the signal strength pointing method. Similar adjustment for polarization alignment does not yield satisfactory results and another method must be employed. The current method for polarization adjustment includes the installer sending a linearly polarized test signal from the end-user terminal to the satellite. The test signal is received by the satellite. A component of the test signal is received in one polarization axis of the satellite and another component of the test signal is received in the other polarization axis of the satellite. The magnitude of the components in each axis is received by the satellite control center. The installer telephones the control center for the results and then adjusts the antenna polarization. Another test signal is sent to the satellite and the process continues until the antenna polarization is aligned with the satellite. This process is very difficult, time consuming and not accurate. Moreover, the designated frequency in both polarization axes of the satellite cannot be used for normal communications during this alignment process. There is therefore a need for a system and method of aligning antenna polarization axes of a dual polarized end-user terminal.
The present invention is a system and method of aligning antenna polarization axes of a dual polarized end-user terminal.
According to the teachings of the present invention there is provided, a method for aligning antenna polarization axes of a dual polarized end-user terminal having an antenna, the antenna being aligned with a satellite in relation to azimuth and elevation, the end-user terminal being configured to produce a first output corresponding to a first component of a received signal parallel to a first polarization axis of the antenna and a second output corresponding to a second component of the received signal parallel to a second polarization axis of the antenna, the first polarization axis being orthogonal to the second polarization axis, the method comprising the steps of: (a) receiving a linearly polarized signal having a frequency wherein for the frequency and during a time period when the signal is being transmitted, the satellite is not transmitting signals with a linear polarization that is orthogonal to the linearly polarized signal; (b) autocorrelating the first output and the second output to produce a measurement of autocorrelation; and (c) adjusting the antenna polarization axes to minimize the measurement of autocorrelation.
According to a further feature of the present invention, the step of autocorrelating is performed by inputting the first output and the second output into an electronic mixer to produce the measurement of autocorrelation.
According to a further feature of the present invention, there is also provided the step of reducing proportionately frequencies of the first output and the second output.
According to a further feature of the present invention, there is also provided the step of tuning the first output and the second output to the frequency.
According to a further feature of the present invention, there is also provided the step of filtering the first output using a first band pass filter and the second output using a second band pass filter.
According to a further feature of the present invention, the step of autocorrelating is performed by inputting the first output and the second output into an electronic mixer and inputting the output of the electronic mixer into a low-pass filter to produce the measurement of autocorrelation.
According to a further feature of the present invention, there is also provided after the step of autocorrelating, the step of displaying the measurement of autocorrelation.
According to a further feature of the present invention, the step of adjusting is performed by actuating an alignment actuator configured to adjust the antenna polarization axes to minimize the measurement of autocorrelation.
According to the teachings of the present invention there is also provided, a system for aligning antenna polarization axes of a dual polarized end-user terminal having an antenna, the antenna being aligned with a satellite in relation to azimuth and elevation, the end-user terminal being configured to produce a first output corresponding to a first component of a received signal parallel to a first polarization axis of the antenna and a second output corresponding to a second component of the received signal parallel to a second polarization axis of the antenna, the first polarization axis being orthogonal to the second polarization axis, the system comprising: (a) a first connection configured for connection to the end-user terminal for receiving the first output; (b) a second connection configured for connection to the end-user terminal for receiving the second output; and (c) an autocorrelation apparatus having a first input and a second input; wherein the first connection is connected to the first input and the second connection is connected to the second input.
According to a further feature of the present invention, the autocorrelation apparatus includes an electronic mixer having a first input that is connected to the first connection and a second input that is connected to the second connection.
According to a further feature of the present invention: (a) the autocorrelation apparatus further includes a low-pass filter having an input; and (b) the electronic mixer has an output that is connected to the input of the low-pass filter.
According to a further feature of the present invention: (a) the low-pass filter has an output; and (b) the input of the display is connected to the output of the low-pass filter.
According to a further feature of the present invention: (a) the autocorrelation apparatus further includes a dual polarized block down-converter having a first input that is connected to the first connection and a second input that is connected to the second connection; and (b) the dual polarized block down-converter is interposed between the first connection, the second connection and the electronic mixer.
According to a further feature of the present invention, there is also provided: (a) a first down-converter that is interposed between the first connection and the electronic mixer; and (b) a second down-converter that is interposed between the second connection and the electronic mixer.
According to a further feature of the present invention, the autocorrelation apparatus includes: (a) a first tuner that is interposed between the first connection and the electronic mixer; and (b) a second tuner that is interposed between the second connection and the electronic mixer.
According to a further feature of the present invention, the autocorrelation apparatus includes: (a) a first band pass that is interposed between the first connection and the electronic mixer; and (b) a second band pass filter that is interposed between the second connection and the electronic mixer.
According to a further feature of the present invention, there is also provided an alignment control system and an alignment actuator wherein the alignment control system is configured to control the alignment actuator to adjust the antenna polarization axes in response to an output of the autocorrelation apparatus.
According to the teachings of the present invention there is also provided, a system for aligning antenna polarization axes comprising: (a) a dual polarized end-user terminal having an antenna and the antenna having an associated first polarization axis and a second polarization axis, wherein: (i) the first polarization axis is orthogonal to the second polarization axis; and (ii) the end-user terminal is configured to produce a first output corresponding to a first component of a received signal parallel to the first polarization axis and a second output corresponding to a second component of the received signal parallel to a second polarization axis; (b) a first connection configured for connection to the end-user terminal for receiving the first output; (c) a second connection configured for connection to the end-user terminal for receiving the second output; and (d) an autocorrelation apparatus having a first input and a second input; wherein the first connection is connected to the first input and the second connection is connected to the second input.
According to a further feature of the present invention, the autocorrelation apparatus includes an electronic mixer having a first input that is connected to the first connection and a second input that is connected to the second connection.
According to a further feature of the present invention: (a) the autocorrelation apparatus further includes a low-pass filter having an input; and (b) the electronic mixer has an output that is connected to the input of the low-pass filter.
According to a further feature of the present invention, there is also provided a display having an input and wherein: (a) the low-pass filter has an output; and (b) the input of the display is connected to the output of the low-pass filter.
According to a further feature of the present invention, there is also provided an alignment control system and an alignment actuator wherein the alignment control system is configured to control the alignment actuator to adjust the antenna polarization axes in response to an output of the autocorrelation apparatus.